Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Oct. 31, 2013		Jul. 31, 2013
Available-for-sale debt securities:
Total available-for-sale securities	$ 1,389		$ 1,979
Liabilities:
Long-term debt	499		499
Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities	500		489
Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities	269		269
U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities	73		69
Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities	32		33
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets:
Assets:	303		917
Available-for-sale debt securities:
Total available-for-sale securities	902		893
Total assets measured at fair value on a recurring basis	1,205		1,810
Liabilities:
Senior notes	561	[1]	560	[1]
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities	500		489
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities	269		269
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities	73		69
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Estimate of Fair Value, Fair Value Disclosure [Member] | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities	32		33
Fair Value, Measurements, Recurring | Level 1
Assets:
Assets:	303		917
Available-for-sale debt securities:
Total available-for-sale securities	32		33
Total assets measured at fair value on a recurring basis	335		950
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring | Level 1 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities	32		33
Fair Value, Measurements, Recurring | Level 2
Assets:
Assets:	0		0
Available-for-sale debt securities:
Total available-for-sale securities	842		827
Total assets measured at fair value on a recurring basis	842		827
Liabilities:
Senior notes	561	[1]	560	[1]
Fair Value, Measurements, Recurring | Level 2 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities	500		489
Fair Value, Measurements, Recurring | Level 2 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities	269		269
Fair Value, Measurements, Recurring | Level 2 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities	73		69
Fair Value, Measurements, Recurring | Level 2 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 2 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3
Assets:
Assets:	0		0
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Total assets measured at fair value on a recurring basis	28		33
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring | Level 3 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Level 3 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities	$ 0		$ 0

[1] Carrying value on our balance sheet at October 31, 2013 was $499 million and at July 31, 2013 was $499 million. See Note 6.